This invention relates to a removable type magnetic recording/reproducing device such as a flexible or floppy disk drive (which may be abbreviated to "FDD") and a motor driving unit for use in the FDD.
As is well known in the art, the FDD of the type described is a device for carrying out data recording and reproducing operation to and from a magnetic disk medium of a flexible or floppy disk (which may be abbreviated to "FD") loaded therein. In recent years, the FDS have been more and more improved to have a larger storage capacity. Specifically, development has been made of the FDs having the storage capacity of 128 Mbytes (which may be called large-capacity FDs) in contrast with the FDs having storage capacity of 1 Mbyte or 2 Mbytes (which may be called small-capacity FDs). Following such development, the FDDs have also been improved to accept the large-capacity FDs for data recording and reproducing operations to and from the magnetic disk media of the large-capacity FDs. Furthermore, the large-capacity FDs have been more improved to have a larger storage capacity of 256 Mbytes, 512 Mbytes, . . . , and so on.
Throughout the present specification, FDDs capable of recording/reproducing data for magnetic disk media of the large-capacity FDs alone will be referred to high-density exclusive type FDDs. On the other hand, FDDS capable of recording/reproducing data for magnetic disk media of the small-capacity FDs alone will be called low-density exclusive type FDDs. Furthermore, FDDs capable of recording/reproducing data for magnetic disk media of both the large-capacity and the small-capacity FDs will be called high-density/low-density compatible type FDDs. In addition, the high-density exclusive type FDDs and the high-density/low-density compatible type FDDs will collectively be called high-density type FDDs.
The low-density exclusive type FDD and the high-density type FDD are different in mechanism from each other in several respects, one of which will presently be described. In either FDD, a magnetic head is supported by a carriage which is driven by a drive arrangement to move in a predetermined radial direction with respect to the magnetic disk medium of the FD loaded in the FDD. The difference resides in the structure of the drive arrangement. More specifically, the low-density exclusive type FDD uses a stepping motor as the drive arrangement. On the other hand, the high-density type FDD uses a linear motor such as a voice coil motor (which may be abbreviated to "VCM") as the drive arrangement.
Now, description will be made as regards the voice coil motor used as the drive arrangement in the high-density type FDD. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coil is disposed on the carriage at a rear side and is wound around a drive axis extending in parallel to the predetermined radial direction. The magnetic circuit generates a magnetic field in a direction intersecting that of an electric current flowing through the voice coil. With this structure, by causing the electric current to flow through the voice coil in a direction intersecting that of the magnetic field generated by the magnetic circuit, a drive force occurs in a direction extending to the drive axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the voice coil motor to move the carriage in the predetermined radial direction.
Another difference between the low-density exclusive type FDD and the high-density type FDD resides in the number of revolution of a spindle motor for rotating the magnetic disk medium of the FD loaded therein. More specifically, the low-density exclusive type FDD may rotate the magnetic disk medium of the small-capacity FD loaded therein at a low rotation speed of either 300 rpm or 360 rpm. On the other hand, the high-density type FDD can admit, as the FD to be loaded thereinto, either the large-capacity FD alone or both of large-capacity FD and the small-capacity FD. As a result, when the large-capacity FD is loaded in the high-density type FDD, the spindle motor for the high-density type FDD must rotate the magnetic disk medium of the large-capacity FD loaded therein at a high rotation speed of 3600 rpm which is equal to ten or twelve times as large as that of the small-capacity FD.
In the meanwhile, the large-capacity FD generally has an external configuration identical with that of the small-capacity FD. Specifically, both of the large-capacity and the small-capacity FDs have a flat rectangular shape of a width of 90 mm, a length of 94 mm, and a thickness of 3.3 mm in case of a 3.5-inch type. However, the large-capacity FD has a narrower track width (track pitch) than that of the small-capacity FD. As a result, it is difficult for the large-capacity FD to position a magnetic head of the high-density type FDD on a desired track in the magnetic disk medium thereof in contrast with the small-capacity FD. Accordingly, a servo signal for position detection is preliminarily written in the magnetic disk medium of the large-capacity FD.
In addition, it is necessary for the high-density/low-density compatible type FDD to identify and detect whether the FD loaded therein is the large-capacity FD or the small-capacity FD.
In the meanwhile, an FD about to manufactured (which will be called a raw FD) comprises merely a magnetic disk medium having both surfaces coated with magnetic material. In order to enable the raw FD to be utilized for an electronic device such as a personal computer or a word processor, it is necessary for the raw FD to partition the magnetic disk medium into a plurality of regions with addresses and to record and manage what information should be written in each region. Such a sequence of processing steps is called a format(ting) or an initialization.
In general, the FD comprises a magnetic disk medium on which a plurality of tracks which are arranged with concentric circles around a center of rotation thereof. The tracks may arranged with a spiral fashion around the center of rotation. Each track is divided in a circumferential direction into a predetermined number of sectors having a length equal to one another.
The formatting is classified into a physical formatting and a logical formatting. The physical formatting determines how data is arranged on the magnetic disk medium. Specifically, the physical formatting determines the total tracks, the total usable tracks, the number of sectors in each track, a medium storage capacity, a format storage capacity, and so on. On the other hand, the logical formatting determines locations where information corresponding to table of contents is written on the magnetic disk medium and assigns addresses to units each of which writes information. The logical formatting is also called a sector formatting.
More specifically, the sector formatting is performed by using a servo writer and a media formatter. The servo writer partitions first each sector into a servo field and a data field to write the above-mentioned servo signal in the servo field. In this event, the sectors on each track are assigned with sector numbers in the circumferential direction in order. Thereafter, the media formatter carries out test of the sector format and preparation of a defective map. Specifically, not that all of the tracks on the magnetic disk medium can be used by a user, an area available to the user is restricted. Such an area is referred to as a user data area. Tracks other than the user data area are used as alternate tracks for alternate sectors for replacing defective sectors in the user data area. Such an area for the alternate tracks is an alternate area. The alternate area is generally disposed in the magnetic disk medium in a radial direction on the inward side. In addition, separation of the tracks into the user data area and the alternate area is carried out by the physical formatting. The media formatter first performs test of the sector format to detect the defective sectors on the user data area. Subsequently, the media formatter carries out rearrangement of the sectors except for the defective sectors. Thereafter, the media formatter prepares a defective map. The defective map is a table for entering information indicating where the defective sectors on the user data area are arranged to which alternate sectors in the alternate area. The defective map is stored in a predetermined sector in the alternate area. If the storage capacity of a sector-formatted FD is less than a predetermined specification storage capacity due to the presence of a lot of defective sectors, the sector-formatted FD is discarded because the sector-formatted FD cannot be used.
As described above, there are various types of the large-capacity FDs so as to have the storage capacity of 128 Mbytes or 256 Mbytes. Throughout the present specification, the large-capacity FD having the storage capacity of 128 Mbytes is called a single-density large-capacity FD while the large-capacity FD having the storage capacity of 256 Mbytes is called a double-density large-capacity FD. Although each of the single-density large-capacity FD and the double-density large-capacity FD has the same line recording density, the same sector format (servo format), and the same number of disk revolution, the single-density large-capacity FD and the double-density large-capacity FD have different track densities from each other. That is, the double-density large-capacity FD has the track density twice as large as that of the single-density large-capacity FD. In addition, the high-density type FDDs capable of recording/reproducing data for magnetic disk media of the single-density large-capacity FDs will be referred to as single-density large-capacity type FDDs. On the other hand, the high-density type FDs capable of recording/reproducing data for magnetic disk media of the double-density large-capacity FDs will be referred to as double-density large-capacity type FDDs.
It is assumed that data are read from the magnetic disk medium of the double-density large-capacity FD by the magnetic head of the single-density large-capacity type FDD. In this event, an output level of the read data is half of that obtained when data on the magnetic disk medium of the single-density large-capacity FD is read by the magnetic head of the single-density large-capacity type FDD. In addition, it is assumed that data are read from the magnetic disk medium of the single-density large-capacity FD by the magnetic head of the single-density large-capacity type FDD. In this event, an output level of the read data is equivalent to that obtained when data on the magnetic disk medium of the double-density large-capacity FD are read by the magnetic head of the double-density large-capacity type FDD.
On the other hand, it is assumed that data are written in the magnetic disk medium of the double-density large-capacity FD by the magnetic head of the single-density large-capacity type FDD. In this event, a recording level of the data is lower than that obtained when data on the magnetic disk medium of the single-density large-capacity FD are written by the magnetic head of the single-density large-capacity type FDD. In addition, it is presumed that data are written in the magnetic disk medium of the single-density large-capacity FD by the magnetic head of the double-density large-capacity type FDD. In this event, a recording level of the data is equivalent to that obtained when data on the magnetic disk medium of the double-density large-capacity FD are written by the magnetic head of the double-density large-capacity type FDD.
However, once data are written in the magnetic disk medium of the single-density large-capacity FD by the magnetic head of the double-density large-capacity type FDD, the data on the magnetic disk medium of the single-density large-capacity FD only have a recording level equivalent to that of the magnetic disk medium of the signal-density large-capacity FD. As a result, when that data on the magnetic disk-medium of the single-density large-capacity FD are read by the magnetic head of the single-density large-capacity type FDD, the read data have an output level which is a half of a normal output level. Accordingly, reading of data on the magnetic disk medium of the single-density large-capacity FD by the double-density large-capacity type FDD is no problem, but writing of data on the magnetic disk medium of the single-density large-capacity FD by the double-density large-capacity type FDD is a problem. It is therefore necessary to make the double-density large-capacity type FDD have compatibility of reproduction for the single-density large-capacity FD alone.
In view of such necessity, it is necessary for the high-density type FDD to determine which type the large-capacity FD loaded therein belongs to.
In order to cope with this problem, Japanese Unexamined Patent Publications of Tokkai (JP-A) Nos. 9-306142 on Nov. 28, 1997, 9-306089 on Nov. 28, 1997, and 9-306143 on Nov. 28, 1997 disclose a large-capacity flexible disk and a high-density type disk drive used therefor. In these publications, a case accommodating the magnetic disk medium of the large-capacity FD is provided not only with a large-capacity identifier hole or notch for discriminating the large-capacity FD from a different-capacity FD but also with selectively formed type identifier holes or notches for identifying the type of the large-capacity FD. In addition, in these publications, the high-density type FDD is provided not only with a large-capacity detecting switch for detecting the presence or absence of the above-mentioned large-capacity identifier hole or notch but also with type detecting switches for detecting the presence or absence of the type identifier holes or notches.
However, the above-proposed high-density type FDD is disadvantageous in that a lot of parts are required because the high-density type FDD must be provided with the type detecting switches for detecting the type of the large-capacity FD.
In addition, Japanese Unexamined Patent Publications of Tokkai (JP-A) Nos. 9-320181 on Dec. 12, 1997 and 9-330556 on Dec. 22, 1997 disclose a control method for a spindle motor for a high-density type flexible disk drive. In these publications, the high-density type FDD comprises a switch unit for detecting whether a loaded FD is a large-capacity FD or a small-capacity FD and a control device for controlling drive of a spindle motor so as to rotate the spindle motor at a high rotation speed when the loaded FD is identified as the large-capacity FD and so as to rotate the spindle motor at a low rotation speed when the loaded FD is identified as the small-capacity FD.
As described above, the high-density/low-density compatible type FDD must rotate in the high speed mode the spindle motor at the high rotation speed which is equal to ten or twelve times as large as that in the low speed mode. In general, it is difficult to control rotation at a high precision with a desired torque using the single spindle motor in the two speed modes which have extremely different rotation speeds.
On the other hand, a technique for enabling control of the rotation speed at the high precision under a constant rotation speed mode is already known. For instance, it is possible to control the rotation speed at the high precision by using a sensorless motor driver in a case of the high rotation speed of 3,600 rpm. Furthermore, it is possible to control the rotation speed at the high precision by using an FG motor driver in a case of the low rotation speed of either 300 rpm or 360 rpm. A three-phase brushless d.c. motor is used as a motor operable at the constant rotation speed mode. In addition, there are two methods of connecting windings in the three-phase brushless d.c. motor, namely, a unipolar connection and a bipolar connection. The unipolar connection is a connection where a common connection terminal of three-phase coils is connected to either a power supply terminal or a ground terminal to allow current to flow through the coil of each phase. The bipolar connection is a connection where the common connection terminal of the three-phase coles is opened to allow current to flow through two coils at a time. The bipolar connection is used in control of the number of revolution under the above-mentioned constant rotation speed mode.
A motor drive is proposed in Japanese Unexamined Patent Publication of Tokkai No. Hei 6-351,283 or JP-A 6-351,283 on Dec. 22, 1994 which is hereby incorporated herein by reference. The motor drive selectively allows switching of the unipolar connection and the bipolar connection in order to allow a single motor to switch a motor characteristics at two rotation speed modes which are operable at a low speed rotation state and a high speed rotation state. The motor drive is used, for example, in a portable magnetic tape recorder to satisfactorily carry out by using the single motor both of a low-speed (a constant-speed) tape travelling mode such as reproduction (playback), recording of a tape, or the like and a high-speed tape travelling mode such as rapid traversing, rewinding of the tape, or the like. In the low rotation speed mode (or in the low-speed tape travelling mode such as the above-mentioned reproduction, recording, or the like), the motor drive selects the bipolar connection to drive the motor with a full wave and it results in a power-saving effect. On the other hand, in the high rotation speed mode (or in the high-speed tape travelling mode such as the above-mentioned rapid traversing, rewinding, or the like), the motor drive selects the unipolar connection to drive the motor with a half wave and this results decreasing the number of revolutions in the motor.
However, it is difficult in the JP-A 6-351,283 to control the number of revolutions (the rotation speed) at the high precision although it is possible to obtain a necessary torque in each of the low rotation speed mode and the high rotation speed mode. This is because it is not necessary for the drive motor to control the number of revolutions at the high precision from the first particularly in the high rotation speed mode which is used in the rapid traversing or the rewinding of the tape.
For example, it is necessary for the high-density/low-density compatible type FDD to have the torque equal to or more than 14 g-cm in the high rotation speed mode and to have the torque equal to or more than 60 g-cm in the low rotation speed mode. In addition, it is necessary for the high-density/low-density compatible type FDD to restrain fluctuations in the number of revolutions within 0.2%.